To his supporters, former MI5 agent David Shayler was the "born rebel" who challenged the establishment.

To an infuriated government he was the spy turned whistleblower who just would not shut up.

He may now have been convicted for his revelations about the workings of MI5 - but few expect the five-year saga to come to a quiet end.

Shayler is hardly the discrete spy of popular fiction.

The portly northerner is a football-fanatic more likely to be seen in his beloved Middlesbrough top than a James Bond dinner jacket.

His headmaster at John Hampden grammar school, Buckinghamshire, described him as "a born rebel who sails close to the wind".

Unorthodox

Shayler did not study at Oxford or Cambridge, and only found his way into the then secretive world of MI5 recruitment by accident.

After failing as a journalist on the Sunday Times, he responded to a peculiar advertisement in the newspaper.

Hello, you're through to the Public Friend Number One Hotline

Shayler's answer phone message

Headlined "Godot isn't coming" - a reference to Samuel Beckett's play Waiting for Godot - it appealed to frustrated people who were "stuck in a rut and unable to progress".

After a few tests at a recruitment agency, Shayler was called to an unmarked building in central London for an interview.

Shayler signed the Official Secrets Act during the first interview and was hired in 1991.

His career in MI5 began unglamorously in the records department, vetting
potential MPs before the 1992 general election.

He later worked for G Branch, dealing with international terrorism and T Branch - targeting terrorism in Northern Ireland.

While serving on the Libya desk, Shayler says a contact in MI6 informed him of an alleged plot to blow up Colonel Muammar Gaddafi.

Unhappy

Desk-bound and increasingly unhappy with his employer, Shayler - or "Frowny" as he was christened by colleagues - quit his job in 1997.

He took his concerns about the UK's secret services to Mail on Sunday journalist Nick Fielding - sparking the biggest spy row since Spycatcher.

Even before the publication of the original allegations- including alleged links between the IRA and Libya and details of several MI5 employees and files - Shayler decided it would be prudent to leave the UK.

He moved first to the Netherlands and later to France - where he relieved his homesickness by ordering pies from a Middlesbrough butcher.

Shayler's partner, former MI5 agent Annie Machon, returned to the UK to test the waters in September 1997. She was arrested, but never charged.

The whistleblower was to see the inside of a prison cell himself the following August.

The Gaddafi plot dismissed as "pure fantasy"

Detained in Paris after the Gaddafi plot claims emerged, Shayler was held while French judges considered extradition proceedings lodged by Scotland Yard.

The UK Government dismissed the allegations as "pure fantasy", but the Paris court agonised over whether Shayler's disclosures were prompted by fears over MI5's conduct or by avarice.

Shayler received £39,000 for talking to the papers, according to the French public prosecutor. The ex-spy put the figure nearer £20,000.

The extradition order was eventually turned down because the UK Government's calls for Shayler's return were deemed to be "politically motivated" - and thus against French law.

With no government compromise in sight, Shayler decided to return to the UK in 2000 and defend his actions.

Legacy

The future for Shayler now rests with the judge.

Should he escape a prison sentence, he has expressed an interest in making a living in letters, either returning to journalism or writing fiction.

While in exile he completed a novel, The Organisation, a tale of sex, spies and football.

And at least one former spy believes his legacy will live on.

"[He has] set in motion an unstoppable momentum towards real reform of the intelligence services," said Richard Tomlinson, a former MI6 agent who also turned whistleblower.